Rapid eye movement (REM) sleep behavior disorder (RBD) is a parasomnia characterized by the loss of normal muscle atonia during REM sleep leading to undesirable and often violent behaviors associated with dream mentation. Idiopathic RBD (iRBD) patients are particularly at risk of developing a synucleinopathy such as dementia with Lewy bodies, Parkinson’s disease or multiple system atrophy. Indeed, subtle signs of neurodegeneration are seen in these patients including a slowing of brain electrical activity (EEG) during wakefulness and the presence of cognitive impairment. The purpose of this thesis is 1) to investigate waking EEG abnormalities specific to RBD patients with mild cognitive impairment (MCI) and 2) to assess the usefulness of baseline EEG spectral analysis performed during wakefulness for predicting the development of a neurodegenerative disease.
The first study compared a group of iRBD patients with MCI to cognitively intact patients and a group of healthy control. Only those with concomitant MCI showed waking EEG slowing in the posterior cortical regions, namely higher relative theta power in the parietal, temporal, and occipital regions, lower relative alpha power in the occipital region, and higher slow-to-fast frequency ratio compared to patients without MCI and controls. Moreover, the spectral ratio negatively correlated with attentional/executive function, visuospatial abilities and verbal episodic memory. The second study compared baseline waking EEG of iRBD patients who developed disease on a mean longitudinal follow-up of 3,5 years with patients who remained disease-free and controls. iRBD patients who developed disease showed higher absolute delta and theta power and higher slow-to-fast power ratio in all five cortical regions compared to disease-free patients and controls. This thesis identified specific EEG abnormalities during wakefulness in iRBD patients with MCI. Moreover, these anomalies are associated with greater short-term risk of developing parkinson’s disease, dementia with Lewy bodies or multiple system atrophy. Therefore, EEG slowing seems to be a promising marker of neurodegeneration in iRBD patients.